The present invention relates to an image processing apparatus, an image processing method, and a network system and, more particularly, to an image processing apparatus and an image processing method, which process input image data and output the processed image data, and a network system to which the image processing apparatus is connected.
An interface of an image processing apparatus is connected to an ATM network that processes color-separated image data and transfers the data in ATM (Asynchronous Transfer Mode) or a local area network (to be referred to as a "LAN" hereinafter) using, e.g., Ethernet for transferring data in a mode other than ATM, and transfers and outputs image data coded by coding methods such as JPEG, MPEG, and the like. The interface does not selectively output color-separated image data themselves and data obtained by coding these data.
However, the above-mentioned technique suffers the following problems.
The image processing apparatus must output image data at a constant rate. In particular, an apparatus having a plurality of image forming means cannot form an image unless image data is output from image processing means at a constant rate.
More specifically, if there are two different types of data, i.e., image data which is obtained by reading an original image and is synchronously input, and image data which has been subjected to variable-length coding such as JPEG, MPEG, and the like, and is input via the ATM network, the image processing apparatus must output these two types of image data at a constant rate.
Furthermore, an image processing apparatus comprising an image memory adopts a method of compressing an image to be stored in the image memory so as to reduce its memory size.
However, the image processing apparatus that performs image compression is not designed in consideration of applications in combination with the above-mentioned network system.
Furthermore, when image data compressed by a lossy compression method such as JPEG, MPEG, or the like is expanded, the decoded image is distorted. In this case, if the compression/expansion is performed only once, deterioration of the image quality falls within an allowable range.
However, since the image processing apparatus comprising the image memory adopts the method of compressing an image to be stored in the image memory so as to reduce its memory size, an input compressed image is expanded, is compressed again by the lossy compression method, and is expanded, thus considerably deteriorating the image quality.
Image compression basically assigns a long code to data with a low input frequency, in variable-length coding, and assigns quantization data with a large step width to such data in fixed-length coding. However, in an image which is temporarily compressed by the lossy compression method and is expanded, it is difficult discriminate whether or not each data is data with a low input frequency, and this difficultly becomes a factor that deteriorates the image quality.
If different compression methods are used, it becomes more difficult to predict the frequency distribution of input image data.